Hydrocracking process for converting heavy hydrocarbon into low sulfur gasoline

ABSTRACT

A hydrocracking process wherein heavy hydrocarbon oils having from about 10 to 50 percent boiling above 1,000*F. and containing appreciable amounts of sulfur, nitrogen, and metal-containing compounds as well as asphaltenes are converted into a minor fraction of low sulfur residual fuel oil and a major fraction of low sulfur gasoline. The process comprises hydrocracking the heavy oil with molecular hydrogen, at a temperature of about 700*-850*F. in the presence of a sulfur and nitrogen resistant hydrocracking catalyst comprising a hydrogenating component supported upon an amorphous inorganic oxide cracking base to convert the heavy hydrocarbon oil into a gas-oil fraction and a low sulfur residual fraction; separating the gas-oil fraction from the residual fraction; hydrocracking the gas-oil fraction with molecular hydrogen, at a temperature of 700*-780*F., in the presence of a sulfur and nitrogen resistant hydrocracking catalyst comprising a hydrogenation component supported upon a cation exchanged crystalline silica-alumina zeolitic molecular sieve cracking base to yield low sulfur, low nitrogen gasoline.

United States Patent 1191 Nelson et a1.

m1 3,891,539 ['45] June 24, 1975 HYDROCRACKING PROCESS FOR CONVERTINGHEAVY HYDROCARBON INTO LOW SULFUR GASOLINE [75] Inventors: GeraldVerdell Nelson, Nederland.

Tex.; Glenn Cooper Wray, Dyersburg, Tenn. [73] Assignee: Texaco Inc.,New York, NY. [22] Filed: Feb. 25, 1974 [21] Appl. No.: 445,365

Related US. Application Data [63] Continuation-impart of Ser. No.212,565. Dec. 27.

1971. abandoned.

[52] US. Cl. 208/59; 208/D1G. 2; 208/52 CT; 208/77; 208/102; 208/215;208/251 H; 252/455 R; 208/254 H [51] Int. Cl. B0lj 11/82; ClOg 13/02[58] Field of Search 208/59 [56] References Cited UNITED STATES PATENTS3.360.457 12/1967 Peck et a1 208/59 3.540.997 11/1970 Hahn et a1. 208/693,551,323 12/1970 Hamblin 208/58 3.562.144 2/1971 Child et a1. 208/593,583,902 6/1971 Masologites et a1. 208/59 3.617.501 11/1971 Eng 208/893.623.974 11/1971 Mounce ct a1... 208/97 3.640.817 2/1972 O'Hara 208/593.684.688 8/1972 Rose1ius.... 208/50 3.723.296 3/1973 Hahn 208/893,773,653 11/1973 Nongbri et a1 208/50 C. G. Ries;

[ 57] ABSTRACT A hydrocracking process wherein heavy hydrocarbon oilshaving from about 10 to 50 percent boiling above 1,000F. and containingappreciable amounts of su1- fur. nitrogen, and metal-containingcompounds as well as asphaltenes are converted into a minor fraction oflow sulfur residual fuel oil and a major fraction of low sulfurgasoline. The process comprises hydrocracking the heavy oil withmolecular hydrogen. at a temperature of about 700-850F. in the presenceof a sulfur and nitrogen resistant hydrocracking catalyst comprising ahydrogenating component supported upon an amorphous inorganic oxidecracking base to convert the heavy hydrocarbon oil into a gas-oilfraction and a low sulfur residual fraction; separating the gas-oilfraction from the residual fraction; hydrocracking the gasoil fractionwith molecular hydrogen. at a temperature of 700-780F.. in the presenceof a sulfur and nitrogen resistant hydrocracking catalyst comprising ahydrogenation component supported upon a cation exchanged crystallinesilica-alumina zeolitic molecular sieve cracking base to yield lowsulfur. low nitrogen gasoline.

13 Claims, 1 Drawing Figure IIYDROCRACKING PROCESS FOR CONVERTING HEAVYHYDROCARBON INTO LOW SULFUR GASOLINE RELATED APPLICATIONS Thisapplication is a continuation-in-part of copending application Ser. No.2l2,565 filed Dec. 27, 1971, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to the hydrocracking of heavy hydrocarbon oils. Particularly, itrelates to hydrocracking heavy hydrocarbon oils having from about 10 to50 volume percent boiling above IOF. and containing appreciable amountsof sulfur, nitrogen, and metalcontaining compounds as well asasphaltenes and other coke forming hydrocarbons. By the process of thisinvention such heavy hydrocarbon oils are converted into a minorfraction of heavy residual fuel oil and a major fraction of low sulfurgasoline. Such gasoline product is suitable for further processing, suchas catalytic reforming or the like, to upgrade the quality and octanenumber. More particularly, the process comprises a two-stage catalytichydrocracking process wherein heavy oil charge is contacted withmolecular hydrogen in a first reaction zone in the presence ofahydrocrack ing catalyst comprising a hydrogenation component selectedfrom the group consisting of Group VI metals, Group VIII metals, theiroxides, their sulfides, and combinations thereof supported upon anamorphous refractory oxide cracking base, at a temperature in the rangeof 700-850F., for conversion of from 50 to 90 volume percent of theheavy hydrocarbon oil into a sulfur and nitrogen containing gas-oilhaving very low metals content without any substantial production ofgasoline; separating the effluent from the first hydrocracking zone intoa gas-oil fraction and a residual fuel fraction; and hydrocracking thegas-oil fraction in a second hydrocracking zone with molecular hydrogenin the presence of a catalyst comprising a hydrogenation componentselected from the group consisting of Group VI metals, Group VIIImetals, their oxides, their sulfides, and combinations thereof supportedupon a refractory metal oxide cracking base such as alumina,silica-alumina, zirconia, titania, cation exchanged crystallinesilica-alumina zeolites, etc., at a temperature in the range of700-780F. for conversion of the sulfur and nitrogen containing gas-oilfraction into a low sulfur and nitrogen containing gasoline.

Within the present specification and claims, the term gas-oil fraction"is meant to include hydrocarbon fractions derived from crude petroleum,shale oil and the like, or from a hydrocarbon conversion process such ashydrocracking; catalytic cracking, thermal cracking, coking, etc., whichfraction boils within the range of from about 430F. to about 1000F. Theterm gas-oil" as used herein is meant to include the light, medium, andheavy gas-oils as those terms are commonly employed in the art. The termgasoline" is meant to include the hydrocarbon fraction boiling in therange of from about 55F. to 430F., or, as it is sometimes expressed, C/430F.". The term dry gas refers to a fraction comprising methane,ethane, and propane when such fraction is separated from normallyliquid, higher boiling hydrocarbons.

Hydrocracking processes for the conversion of heavy hydrocarbon oilsinto lower boiling fractions are well known. Examples of suchhydrocracking processes may be found in such sources as US. Pat. Nos.3,640,817; 3,617,50l; 3,583,902; 3,562,144; 3,551,323; 3,540,997;3,360,457; and 3,254,017. In such hydrocracking processes, it isrecognized that when a heavy hydrocarbon oil with a substantial volumeboiling above IOOOF., and containing substantial amounts of asphaltenes,sulfur, nitrogen, and metal-containing organic compounds, is treated inthe presence ofa hydrocracking catalyst, such compounds act as catalystpoisons. In addition, compounds of such metals as vana dium, iron,nickel, sulfur, etc., which generally are present in such hydrocarbonoils tend to deposit ash and metals upon the hydrocracking catalystwhich increases the rate of coke formation and deposition, therebyinterfering with catalytic activity by covering the active catalyticsites.

Efforts have been made to minimize the poisoning effects and catalystdeactivating effects of such sulfur, nitrogen, and metal compounds. Forinstance, U.S. Pat. No. 3,254,017 describes a hydrocracking processwherein a heavy hydrocarbon oil is sequentially treated in twohydrocracking zones. In the first hydrocracking zone, the heavyhydrocarbon oil is partially hydrocracked to gas-oil and is partiallydesulfurized and denitrogenated with molecular hydrogen in the presenceof a selected catalyst. The catalyst selected for the firsthydrocracking zone comprises a hydrogenation component selected fromGroup VI metals, Group VIII metals, their oxides, their sulfides andmixtures thereof supported upon an amorphous refractory oxide crackingbase having large pore openings in the range of at least 20 up to 200angstrom units and preferably larger, such base being selected fromalumina, silica-alumina, zirconia, titania, etc. Such a large pore,amorphous cracking base has a capacity for adsorbing or otherwisecollecting substantial quantities of ash and metals such as vanadium,nickel, iron and copper without destroying the hydrocracking activity ofsuch catalyst. Effluent from such a first hydrocracking zone, comprisinga gasoil fraction and unconverted residual fraction, is then treated ina second hydrocracking zone under conditions such that a substantialportion of the gas-oil fraction is hydrocracked into lower boilingfractions such as gasoline but with a limitation upon operatingconditions such that not more than a strict upper limit of 30 volumepercent of the unconverted residual fraction is hydrocracked into lowerboiling fractions. To obtain the desired hydrocracking of the gas-oilfraction without substantial hydrocracking of the residual fraction, asecond selected hydrocracking catalyst is employed in the secondhydrocracking zone. Such second catalyst comprises a hydrogenationcomponent selected from Group V] metals, Group VIII metals, theiroxides, their sulfides, and mixtures thereof, supported upon a crackingbase comprising a cation exchanged crystalline silica-alumina zeolitecontaining cations selected from hydrogen, ammonia, divalent metals suchas calcium, magnesium and zinc, and rare earth metals, and containingless than about 5 percent sodium. Such second selected catalyst hasuniform pore openings in the limited range of 5-20 angstroms such thathydrocarbon molecules contained in the residual fraction will not enterthe catalyst pores to be hydrocracked. By limiting the access of theresidual fraction hydrocarbons, the

accumulation of coke, ash, and metal within the second hydrocrackingcatalyst is reduced such that the hydrocracking activity of the secondcatalyst is not severely affected by such accumulation. Effluent fromthe second hydrocracking zone is separated into desired productfractions such as dry gas, gasoline, and heavy fuel oil. Unconvertedresidual fraction may be recycled to the first reaction zone andunconverted gas-oil may be recycled to the second hydrocracking zone.Thus, while recognizing the deleterious effect of metals and cokeaccumulation upon a gas-oil hydrocracking catalyst, the method of US.Pat. No. 3,254,017 attempts to prevent such metal and ash deposition bystrictly limiting conversion in the second hydrocracking zone.Consequently, high yields of gasoline are difficult or impossible toobtain by hydrocracking heavy hydrocarbon oils according to thisprocedure.

In US. Pat. No. 3,562,!44 a process is taught wherein heavy hydrocarbonoil, containing nitrogen, sulfur, and 1 percent or more Conradson Carbonis hydrocracked in a first hydrocracking zone to yield substantialamounts of gasoline; and wherein fractions of the first reaction zoneeffluent boiling above gasoline are hydrocracked in a second reactionzone to yield substantial amounts of high quality jet fuel. Ahydrocracking catalyst comprising sulfided nickel and tungsten upon azeolitic refractory metal oxide cracking base is employed in the firstreaction zone, and in the second hydrocracking zone a catalystcomprising noble metal (platinum or palladium) upon a refractory metaloxide cracking base is employed. Since platinum and palladium are verysensitive to sulfur and nitrogen, reaction conditions in the firstreaction zone must be sufficiently severe to remove a substantialportion of the sulfur and nitrogen contained in the hydrocarbon oilcharge. No account is taken, in US. Pat. No. 3,562,144, of the effect ofmetals and ash upon the activity of the catalyst in the firsthydrocracking zone. Metals and ash deposited upon the catalyst causeincreased production of coke, and under the severe reaction conditionsof the first hydrocracking zone coke production is substantial, causingrapid catalyst deactivation.

A combined hydretreating-hydrocracking process for whole crude oil isdisclosed in US. Pat. No. 3,6l7,50l. In one embodiment, whole crude oilis hydrotreated for removal of sulfur and nitrogen compounds in ahydrotreating zone; hydrotreating effluent is fractionated into lightproduct fractions, a heavy gas oil fraction and, a low sulfur fuel oilfraction; and the heavy gas oil is hydrocracked into additional lightproducts. By following the disclosed process a very substantial portionof the gas-oil component of the crude oil can be converted to gasoline,however the residual fraction of the crude oil, boiling above lOF.remains substantially unconverted, and is recovered from the process asa low value fuel oil product.

It has been observed in the hydrocracking of heavy hydrocarbon oilscontaining sulfur, nitrogen and compounds of metals such as nickel,vanadium and iron, that, although the hydrocracking activity may bemaintained by properly selecting a first hydrocracking zone catalyst,such catalyst rapidly loses its activity to convert sulfur and nitrogencompounds. Particularly, it has been noted that at temperatures of about790F. and higher desulfurization and denitrogenation activity of suchcatalyst undergoes a very rapid decline with increased temperature. Ithas also been noted that at temperatures of about 790F. up to about850F. the activity of such catalyst to hydrocrack heavy oils into lowerboiling gas oil fractions is not substantially effected. The decline indesulfurization activity has been observed to be greater for lowermolecular weight sulfur compounds than for higher molecular weightsulfur compounds. Consequently, we have discovered that cffluent fromthe first hydrocracking zone may be separated into a relatively lowsulfur residual fraction and a sulfur and nitrogen containing gas-oilfraction. Substantial amounts of metals are removed in the firsthydrocracking zone, such that the gas-oil fraction contains only minoramounts of metals even though the residual fraction may still contain anappreciable concentration of metals. If the entire liquid effluent froma first hydrocracking zone is passed into a second hydrocracking zone,the metals, ash, coke, asphaltenes, etc. contained in the residualfraction will accumulate upon the second reaction zone catalyst therebyrequiring increased temperatures to maintain the desired hydrocrackingactivity for the conversion of gas-oil. However, as above noted, as thereaction temperature exceeds about 790F., the desulfurization anddenitrogenation activity of hydrocracking catalyst declines veryrapidly, without a concomitant decline in the hydrocracking activity ofsuch catalyst. Consequently, even though a relatively efficientconversion of heavy hydrocarbon oils into gasoline may be obtained byemploying two hydrocracking zones in sequential alignment, the gasolineproduct from such a process may contain substantial amounts of sulfurand nitrogen compounds, particularly when the catalyst has been inservice for a period such that the reaction temperature of the secondhydrocracking zone has been increased to a temperature above about 790F.in order to maintain the hydrocracking activity of the secondhydrocracking catalyst.

SUMMARY OF THE INVENTION Now according to the method of the presentinvention, we have discovered an improved process for the conversioninto gasoline of a heavy hydrocarbon oil comprising from 10 to 50 volumepercent hydrocarbon boiling above l000F. and containing at least 1percent Conradson Carbon, asphaltenes, about 0.1 to 8 percent sulfur,about I00 to over 1000 ppm nitrogen, as well as nickel, vanadium andiron compounds. According to the process of the invention, such ahydrocarbon oil charge is hydrocracked in a first hydrocracking zone toyield a major portion of a low metals content, sulfur and nitrogencontaining gas-oil fraction, and a partially desulfurized residualfraction boiling above I00OF. under hydrocracking conditions wherein nomore than percent of the hydrocarbon oil charge residual fractionboiling above l000F. is converted to gas-oil and wherein 5 percent orless hydrocracked gasoline is produced; and wherein the gas-oil fractionis hydrocracked in a second hydrocracking zone with molecular hydrogenat a temperature of from about 700-780F. in the presence of a sulfur andnitrogen resistant hydrocracking catalyst to yield low sulfur, lownitrogen content gasoline.

Catalyst selected for the first hydrocracking zone comprises ahydrogenation component selected from Group VI metals, Group VIIImetals, their oxides, their sulfides, and mixtures thereof supportedupon an amorphous inorganic oxide cracking base. Such cracking base isselected such that it has pore openings of from at least about to 200angstroms and preferably larger. so a substantial portion of metalcontaminants which may be present in the heavy hydrocarbon oil charge,may be adsorbed within such cracking base without severely affecting thehydrocracking activity of the first hydrocracking catalyst.

By separating the first hydrocracking reaction zone effluent into agas-oil fraction and residual oil fraction, a portion of the residualoil may be recirculated to the first reaction zone for conversion intoadditional gas-oil fraction. However, we have discovered that theconversion of heavy hydrocarbon oil charge residual fraction boilingabove IOOOF. into gas-oil fraction boiling below 1000F. should belimited to a maximum of about 90 volume percent, and preferably no morethan 80 volume percent. In the event that conversion of the residualfraction of the heavy hydrocarbon oil charge is carried out to more thanabout 90 volume percent, asphaltenes and other heavy hydrocarbonmaterials contained in the hydrocarbon oil charge tend to precipitateonto the first cracking catalyst, thereby preventing access ofconvertible hydrocarbons to the active catalytic sites. Also, we havediscovered that controlling hydrocracking severity in the firsthydrocracking zone to a severity such that no more than 5 percent, andpreferably less gasoline is produced therein, improves desulfurizationof residual fuel oil, lengthens catalyst life, and reduces the rate ofcoke deposition upon the first zone hydrocracking catalyst.Additionally, any gasoline produced in the first hydrocracking zone willcontain substantial amounts of undesirable nitrogen and sulfur compoundssuch that reduction of gasoline production from the first hydrocrackingzone substantially improves the quality of gasoline recovered from thisprocess.

The gas-oil fraction, recovered from the effluent of the firsthydrocracking reaction zone, contains sulfur and nitrogen compounds, butis relatively free of metal compounds, such as the compounds of nickel,vanadium and iron. Therefore, the gas-oil fraction may be ratherseverely hydrocracked and simultaneously desulfurized and denitrogenatedin the second hydrocracking zone to form desulfurized and denitrogenatedgasoline, by employing a second hydrocracking catalyst which maintainsits activity in the presence of sulfur and nitrogen compounds andemploying temperatures in the range of 700780F. Such secondhydrocracking catalyst is comprised of a hydrogenation componentselected from the Group V] metals, Group VIII metals, their oxides,their sulfides, and mixtures thereof, supported upon a refractory metaloxide cracking base. The cracking base may be in the amorphous form,such as alumina, silica-alumina, zirconia, silica-zirconia,silica-titania, etc., or the cracking base may comprise a crystallinesilica-alumina zeolite wherein the sodium cations have been exchangedfor cations selected from hydrogen, ammonia, calcium, magnesium, zinc,etc.

By maintaining the reaction temperature, within the second hydrocrackingzone, in the range of 700-780F. the gas-oil fraction may be hydrocrackedinto gasoline and simultaneously desulfurized and denitrogenated. Attemperatures above about 780F., the desulfurization and denitrogenationactivity of the preferred second hydrocracking catalyst declinesrapidly.

By following the method of the present invention. a heavy hydrocarbonoil containing sulfur, nitrogen, and metal compounds may be convertedinto gasoline which is low in sulfur and nitrogen content and which isessentially free of metal contaminants. Such gasoline is suitable forfurther treatment, such as in a catalytic reforming unit, to improve thequality and octane number thereof.

BRIEF DESCRIPTION OF THE DRAWING The attached drawing is a schematicrepresentation of a process for carrying out the method of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION Heavy hydrocarbon oil chargestocks within the contemplation of the present invention include thosehydrocarbon oils comprising from [0 to 50 volume percent of a residualfraction boiling above 1,000F. and containing at least about I weightpercent Conradson Carbon, from 0.1 to 8 percent sulfur, and from 100 to1000 ppm or more nitrogen. Examples of such heavy hydrocarbon oilsinclude total crudes, atmospheric and vacuum residuum, shale oils, tarsand oils, petroleum residues, coal tar, heavy coker distillates, heavycatalytically cracked recycle stocks, etc. Such hydrocarbon oils maycontain substantial amounts, from 50 to 1000 ppm and more, metalcompounds such as organometallic compounds of vanadium, nickel, iron,copper, etc. Such heavy hydrocarbon oils may also contain substantialamounts of refractory hydrocarbons such as asphaltenes and other highmolecular weight hydrocarbons which may lead to the deposition of cokeupon the hydrocracking catalyst.

The hydrogen which is employed with such heavy hydrocarbon oils in thefirst hydrocracking zone and the gas-oil fraction in the secondhydrocracking zone need not be I00 percent pure. Conveniently, hydrogenfrom the reaction zones is recirculated within the process to conservethe consumption of hydrogen, and only sufficient fresh hydrogen isvented from the process to maintain hydrogen purity in the range ofabout percent or higher. Sources of hydrogen commonly available within arefinery such as catalytic reformer hydrogen with a purity of aboutpercent or higher are suitable as sources of makeup hydrogen for theprocess to replace the hydrogen consumed in the reactions and that whichis vented.

According to this invention, in the first hydrocracking zone, a majorportion of the heavy hydrocarbon charge is hydrocracked into a gas-oilfraction without substantial production of lighter hydrocarbons such asgasoline and dry gas. An effective temperature range for this conversionis from about 700F. to about 850F. In order to limit coke depositionupon the catalyst in the first hydrocracking zone, it is desirable tomaintain a sufficient hydrogen partial pressure to saturate a largepercentage of the unsaturated hydrocarbons which result from crackinghigh boiling hdrocarbons into lower boiling hydrocarbons. The desiredhydrogen partial pressure may be maintained by utilizing hydrogen tohydrocarbon ratios in the range of from about L000 to about 15,000standard cubic feed per barrel and operating pressures of from about 500to about 3,000 psig. Liquid hourly space velocity (LHSV), expressed asvolumes of oil per hour per volume of catalyst (Vo/Hr/Vc) of from about0.1 to about l may be utilized. Preferably, LHSVs in the range of 0.3 to5.0 are employed to obtain a relatively long reac tion period before thecatalyst must be regenerated.

Hydrocracking catalysts which may be employed in the first hydrocrackingzone comprise those hydrocracking catalysts which are sulfur andnitrogen resistant, and which can maintain hydrocracking activity in thepresence of relatively large amounts of metal compounds such as arecommonly found in heavy hydrocarbon oils. Such a first hydrocrackingcatalyst comprises a hydrogenation component supported upon a refractorymetal oxide cracking base. The hydrogenation component may be selectedfrom Group Vl metals, Group VIII metals, their oxides, their sulfides,and

mixtures thereof. Preferably, the hydrogenation component comprises aGroup Vl metal oxide or sulfide in combination with a Group VIII metaloxide or sulfide. Examples of particularly preferred hydrogenationcomponents include cobalt-molybdenum sulfide mixtures,nickel-cobalt-molybdenum sulfide mixtures, and nickel-molybdenum sulfidemixtures. Examples of other combinations which may be effectivelyemployed include nickel-cobalt mixtures, nickel oxide-cobalt oxidemixtures, nickel oxide-cobalt oxide-molybdenum oxide mixtures, andnickel cobalt-molybdenum mixtures. When a Group V] metal or its oxide orsulfide is employed as a hydrogenation component, it is preferable thatsuch metal be present in an amount of from about 5.0 to about 25.0weight percent of the total catalyst. When a Group VIII metal, or itsoxide or sulfide, is employed as the hydrogenation component, it ispreferable that such metal be present in an amount from about 0.3 toabout 8.0 weight percent of the total catalyst. When Group V] and GroupVIII metals, their oxides, or their sulfides are employed incombination, it is preferred that the Group V! metal be present in anamount from about 5.0 to about 25.0 weight percent and the Group Vlllmetal be present in an amount from about 1.0 to about 8.0 weight percentof the total catalyst.

The refractory metal oxide cracking bases which may be employed in thefirst hydrocracking zone include those amorphous oxides having crackingactivity and which have relatively large pore openings in the range ofto 200 angstroms and larger suitable for adsorption of substantialamounts of metal compounds and coke from the hydrocarbon charge oilwithout substantially affecting the hydrocracking activity. Examples ofsuch amorphous cracking bases include alumina, silicaalumina,silica-zirconia, silica-titania, mixtures thereof, etc. At thetemperatures and space velocities specified herein, such amorphouscracking bases having good cracking activity are useful for converting amajor portion of the hydrocarbon oil charge boiling above about 1000F.into gas-oil boiling in the range of 430F.-l000F. without substantialproduction of gasoline and dry gas. Under such operating conditions,coke production is substantially decreased over more severe conditions,thus extending the useful life of the first hy drocracking catalyst.

By employing such selected catalyst in the first hydrocracking zone, thegas-oil conversion product of the heavy hydrocarbon charge issubstantially demetalized. However, with accumulation of metals and cokeupon the catalyst, it is necessary to increase the reaction zonetemperature incrementally in order to maintain the desired hydrocrackingof the heavier fraction of the hydrocarbon charge oil into gas-oilfraction. As the hydrocracking reaction temperature exceeds about 790F.,desulfurization and denitrogenation activity of the first selectedhydrocracking catalyst decreases rapidly. It has been noted that suchdecline in desulfurization activity is proportionally greater for oilsboiling in the gas-oil range than for residual fractions. Therefore,even though desulfurization activity of the first hydrocracking catalystdeclines at temperatures above 790F., the residual fraction effluentfrom the first hydrocracking reaction zone is still substantiallydesulfurized and may be recovered, if desired, as a relatively lowsulfur content heavy fuel oil containing from about 1 percent or lesssulfur. Hydrocracking reaction temperatures below 700F. are notpreferred, as conversion of heavy hydrocarbon oils into the desiredgas-oil fraction is not substantial, thus requiring recycle of largevolumes of unconverted residual fraction to the first reaction zone.Reaction temperatures above about 850F. are not desirable because, atthese temperatures, substantial amounts of the heavy hydrocarbon oil areconverted into low quality sulfur containing gasoline and dry gas.

It has been found that conversion of the residual fraction of ahydrocarbon charge oil greater than about 90 volume percent into gas-oilfraction boiling below l000F. is undesirable. At conversions of about 90percent or greater, asphaltenes and other high molecular weighthydrocarbon components of the heavy hydrocarbon charge oil precipitatein the reaction zone and collect upon the surface of the firsthydrocracking catalyst. The precipitated asphaltenes and high molecularweight hydrocarbons form tarry films and coke upon the surface of thehydrocracking catalyst, effectively blinding the reactive catalyticsites, such that reactant hydrocarbons may not contact such activesites. Therefore, it is within the contemplation of the presentinvention that conversion of the residual fraction of heavy hydrocarboncharge oil into gas-oil range hydrocarbons boiling below l000F. notexceed about 90 volume percent and preferably, such conversion bemaintained at not more than about 80 percent of the heavy hydrocarboncharge.

A portion of the unconverted residual recycle fraction boiling aboveI000F. may be withdrawn from the process to maintain conversion of theheavy hydrocarbon charge within the desired range. Such residual recyclefractions may be employed as a heavy fuel oil, and since thedesulfurization activity of the first hydrocracking catalyst remainsmore effective for the recycle fraction than for the gas-oil fraction attemperatures above 790F., the residual recycle fraction which is yieldedfrom the process is relatively low in sulfur content, containing aboutone percent or less sulfur.

Efi'luent from the first hydrocracking zone may be separated, in a highpressure separation zone, into a first gas fraction comprising hydrogenand a liquid fraction. The hydrogen containing gas fraction may berecirculated to the inlet of the first hydrocracking reaction zone forcontact with additional amounts of heavy hydrocarbon oil charge. Aportion of the recycle gas may be vented to remove hydrogen sulfide,ammonia, and low boiling hydrocarbons in order to maintain the recyclegas hydrogen concentration at the desired value of about percent orhigher. Additional hydrogen may be added to the recycle gas to replacethat consumed in the reaction and that vented from the process.

Liquid from the first high pressure separator, comprising residualfraction, gas-oil fraction, and a small amount of gasoline and dry gasis passed into a fractionation zone. In the fractionation zone, theresidual frac' tion, the gas-oil fraction, the gasoline and dry gas areseparated. A portion of the residual fraction may be recycled from thefractionation zone to the inlet of the first hydrocracking zone forconversion into additional amounts of gas-oil fraction. An amount of theresidual oil fraction is recovered from the fractionation zone such thatthe conversion of the residual fraction of the heavy hydrocarbon oilcharge to gas-oil fraction boiling below l000F. is not greater thanabout 90 volume percent, and preferably not greater than about 80 volumepercent.

The gas-oil fraction from the fractionation zone contains substantialamounts of sulfur and nitrogen compounds and only very small or traceamounts of metal contaminants. Such gas-oil fraction is passed from thefractionation zone to the second hydrocracking zone for conversion intogasoline. If the heavy hydrocarbon charge oil is particularly heavy,containing from about 30 to about 50 percent residual hydrocarbonsboiling above lO0F., it is desirable to recycle a small portion of thegas-oil fraction to the inlet of the first hydrocracking zone as aviscosity cutting oil for the heavy hydrocarbon charge. Such gas-oilfraction used as viscosity cutting oil in the first reaction zone servesalso as a wash oil, and helps prevent accumulation of coke, tar andother high molecular weight hydrocarbons upon the surface of the firsthydrocracking catalyst.

In the second hydrocracking zone, the gas-oil fraction is treated withmolecular hydrogen in a hydrogen to hydrocarbon ratio of from about1,000 to about 10,000 standard cubic feet per barrel (scf/b) at atemperature of from about 700780F., a pressure of from about 500 toabout 2,500 psig, in the presence ofa sulfur resistant hydrocrackingcatalyst at a liquid hourly space velocity of from about 0.5 to about8.0 Vo/Hr/Vc for conversion of said gas-oil fraction into a desulfurizedand denitrogenated gasoline fraction boiling in the range of 55F. to430F.

Temperatures in the range of from about 700-780F. are preferred in thegas-oil hydrocracking reaction because at temperatures below about 700F.the rate of hydrocracking and desulfurization of the gas-oil fraction istoo low to be economical and at temperatures of about 790F. and higherthe desulfurization and denitrogenation activity of hydrocrackingcatalysts declines rapidly. The hydrogen to hydrocarbon ratio andpressure are maintained within the described limits in order to providea hydrogen partial pressure sufficient to promote hydrogenation ofcracked hydrocarbons and promote desulfurization and denitrogenation ofthe gasoline fraction.

Catalysts useful within the second hydrocracking zone have hydrocrackingactivity and are resistant to sulfur and nitrogen poisoning. Suchhydrocracking catalysts comprise a hydrogenation component selected fromGroup V! metals, Group VIII metals, their oxides, their sulfides, andmixtures thereof. When Group Vl metals, their oxides or their sulfidesare employed, such metals are preferably present in an amount from about5.0 to about 25.0 weight percent of the total catalyst. When Group VIIImetals are employed as hydrogenation components, such metals arepreferably present in an amount from about 0.3 to about 8.0 weightpercent of the total catalyst. When Group VI and Group VIII metals, ortheir compounds are used in combination, Group Vl metals are preferablypresent from about 5.0 to 25.0 weight percent of the catalyst and GroupVIII metals are present in an amount of from about 1.0 to 8.0 weightpercent of the catalyst. Examples of hydrogenation components which areeffective in the second hydrocracking zone include a nickel-tungstencombination, a nickel-oxide-tungsten oxide combination, anickel-sulfide-tungsten sulfide combination, a cobalt sulfide-molybdenumsulfide combination, and a nickel sulfide-cobalt sulfide-molybdenumsulfide combination. Such hydrogenation components are supported upon arefractory metal oxide cracking base. Such cracking base may be selectedfrom amorphous metal oxides such as alumina, silica-alumina,silica-zirconia, silica-titania, etc.; from cation exchanged crystallinesilica-alumina, zeolitic molecular sieves; and from mixtures thereof.Preferably, for the zeolitic molecular sieves, cations such as hydrogen,ammonia, calcium, magnesium, zinc, etc. have been exchanged thereinuntil the sodium ion content is less than 5 percent and preferably lessthan I percent. A particularly effective hydrogenation component for thesecond hydrocracking catalyst comprises a mixture of about 4.0-8.0weight percent nickel sulfide and about 9.0-25.0 weight percent tungstensulfide supported upon a cracking base. A particularly effectivecracking base comprises 40 to 85 percent amorphous silica-alumina havinga silica/alumina ratio of from about 2:1 to about 9: l and about [5 to60 percent ofa hydrogen or amm onia exchanged, type Y crystallinesilica-alumina zeolitic molecular sieve having uniform pore openings inthe range of from about 5 to about 20 angstrom units, and having lessthan 1 percent sodium content.

Effluent from the second hydrocracking zone is separated into a secondgas fraction comprising hydrogen and a liquid fraction in a second highpressure separation zone. The second gas fraction may be recycled to theinlet of the second hydrocracking zone in order to conserve hydrogen.When the second gas fraction is recycled, a portion may be vented toremove hydrogen sulfide, ammonia, and low molecular weight hydrocarbonsfrom the system thereby maintaining hydrogen purity within the desiredrange of about percent or higher. Makeup hydrogen may be added to therecycle gas to replace hydrogen consumed in the second hydrocrackingzone and that vented.

The liquid component of the second hydrocracking reaction zone effluentcomprises unreacted gas-oil fraction, gasoline and dry gas. The gasolineis desulfurized and denitrogenated and is suitable for furtherprocessing, such as catalytic reforming, to improve the quality andoctane number thereof. The gasoline is separated from the liquidfraction and unconverted gas-oil may then be recycled to the secondhydrocracking zone, along with gas-oil fraction from the firsthydrocracking zone, for conversion into additional amounts of gasoline.It is contemplated that the unconverted gas-oil fraction may be recycledto the second hydrocracking zone to extinction, such that the entiregas-oil fraction charged from the first hydrocracking zone to the secondhydrocracking zone is completely converted into gasoline and dry gas.

Conveniently, liquid effluent from the second hydro cracking zone may becharged to the fractionation zone for separation into its componentfractions. [n such a case, liquid effluent from the first hydrocrackingzone and liquid effluent from the second hydrocracking zone are chargedto the fractionation zone wherein they are separated into a residualfraction, a gasoil fraction, dry gas and gasoline. A portion of theresidual fraction is yielded to limit conversion of heavy hydrocarboncharge to 90 volume percent or less, and the remaining residual fractionmay be recycled to the first hydrocracking zone for conversion intoadditional gas-oil fraction. The gas-oil fraction from the fractionationzone is charged to the second hydrocracking zone. The gasoline and drygas are recovered as products from the fractionation zone.

The process of the present invention may be further understood byreference to the attached drawing, which is a schematic diagram of apreferred embodiment of the invention. For clarity, many elementscommonly found in a commercial process such as pumps, valves,instrumentation, etc. not necessary for a proper description of thepresent invention have been omitted. It is to be understood that suchdrawing is intended to demonstrate the invention only and is notintended to limit such invention in any manner.

Referring now to the drawing, a residuum hydrocarbon containing up toabout weight percent sulfur, 1 weight percent nitrogen, 600 ppmvanadium, 100 ppm nickel and 200 ppm iron, charged at a rate of about1000 barrels per hour (B/H) in Line 1 is mixed with 400 B/H of residualfraction recycle from Line 2, a gasoil fraction wash stream from Line 3and a recirculating hydrogen gas stream from Line 4 to form a firstreaction mixture, at a pressure of about 2,000 psig, a hydrogen tohydrocarbon ratio of about 10,000 scf/b, and a temperature of about780F., which is contacted with a first hydrocracking catalyst comprisingabout 2.0 weight percent cobalt and about 10.0 weight percent molybdenumsupported upon an amorphous silicaalumina base having pore openings offrom about to about 1,000 angstroms. The reaction mixture contacts thehydrocracking catalyst at a LHSV of about 0.5 vo/hr/vc.

From the first hydrocracking zone, an effluent stream is withdrawn vialine 6 and passes into a first high pressure separation zone 7 wherein afirst gas fraction comprising hydrogen is separated from a first liquidfraction. A portion of the first gas fraction is vented from the firsthigh pressure separation zone via line 8 to maintain the concentrationof hydrogen within the first gas fraction at about 75 volume percent orhigher. The remainder of the first gas fraction passes from the highpressure separator 7 via line 9 to compressor 10. From compressor 10 thefirst gas fraction is recycled via line 4 for combination withadditional amounts of residuum charge to form a reaction mixture forcharge to the first hydrocracking zone 5, as hereinabove described.Makeup hydrogen of about 85 percent purity or higher is added to therecycle gas in line 4 via line 11 to make up for the amount of hydrogenconsumed in the first hydrocracking zone and for the amount of hydrogenvented via line 8. From the first high pressure separation zone a firstliquid fraction is transferred via line 12 and is combined with a secondhydrocracking zone liquid effluent (as will hereinafter be furtherdescribed) from line 13. The combined hydrocracking zone liquideffluents pass via line 14 into fractionation zone 15 wherein they areseparated into a residual fraction, a gas-oil fraction, gasoline and drygas. From fractionation zone 15, residual fraction is withdrawn via line16 and a portion of the residual fraction, at a rate of about 400 B/H isrecycled via line 2 for combination with additional amounts of residuumas hereinbefore described. The remainder of the residual fraction at arate of about 200 B/H is withdrawn from the process via line 17 as aheavy fuel oil, containing about 1.0 weight percent sulfur. Suchresidual fraction is withdrawn as fuel oil at such a rate to maintainthe overall conversion of hydrocarbon oil charge boiling above I000F.into gasoil boiling below 1000F. to about volume percent or less.

The gas-oil fraction, containing about 0.5 weight percent sulfur andabout ppm nitrogen, is withdrawn from fractionator 15 via line 18. Asmall portion ofgasoil fraction at a rate of about 50 B/H is transferredfrom line 18 via line 3 to the inlet of the first hydrocracking zone asa wash-oil stream as has hereinabove been described. The remainder ofthe gas-oil fraction is mixed with the second recirculating gas streamfrom line 19 to form a second reaction mixture and is passed into secondhydrocracking zone 20. In second hydrocracking zone 20, the secondreaction mixture at a temperature of about 750F., a pressure of about1,500 psig, a hydrogen to hydrocarbon ratio of about 7,500 scf/bcontacts a second hydrocracking catalyst comprising about 6.0 weightpercent nickel sulfide and about 19 weight percent tungsten sulfidehydrogenation component supported upon a hydrogen exchanged crystallinesilica-alumina zeolitic molecular sieve having pore openings of fromabout 5 to about 20 angstrom units, at an LHSV of about 1.5 vo/hr/vc todesulfurize, denitrogenate, and convert said gas-oil fraction intogasoline. Effluent from the second hydrogenation zone 20 is passed vialine 21 into a second high pressure separator 22 wherein the effluent isseparated into a second gaseous fraction and a second liquid fraction. Aportion of the second gaseous fraction is vented via line 23 to removehydrogen sulfide, ammonia, and low boiling hydrocarbons from the systemand the remainder of the second gaseous fraction passes via line 24 intocompressor 25. From compressor 25 the second gaseous fraction passes assecond recycle gas into line 19 for combination with additional gas-oilfraction as hereinabove described. Makeup hydrogen to replace thehydrogen consumed in the second hydrocracking zone and the hydrogenvented via line 23 is added via line 26 to the second recycle gas streamin line 19.

Liquid component of the second hydrocracking zone effluent passes fromthe second high pressure separator 22 via line 13 for admixture withfirst hydrocracking zone liquid effluent in line 14 as hereinabovedescribed. [n the fractionation zone 15 a dry gas comprising methane,ethane, and propane is separated and removed at a rate of about 250,000scf/h via line 27. A gasoline stream is separated in fractionation zone15 for recovery as a product. Such gasoline, at a rate of 825 Elf! andcontaining about 20 ppm sulfur and 2 ppm nitrogen, is recovered via line28. The gasoline product has an octane rating of 65 research octaneclear, and is suitable for use as a charge stock to an octane improvingprocess such as, for example, catalytic reforming.

Thus, the present invention provides a novel method for treating ahydrocarbon oil, containing substantial amounts of sulfur, nitrogen, andmetal compounds, to produce a low sulfur gasoline product and a lowsulfur heavy fuel oil product. Obviously. many variations andmodifications which may be made without departing from the spirit andscope of the present invention will occur to those skilled in the art.Therefore, no limitations to the present invention are intended exceptsuch limitations as are embodied in the appended claims.

We claim:

1. A hydrocracking process wherein heavy hydrocarbon oil chargecontaining 0.1 to 8 percent sulfur, l to 1000 ppm and more nitrogen, andI00 ppm and more compounds of nickel, vanadium, iron, and copper, andcomprising from about 10 to 50 volume percent residual fraction boilingabove l000F. are converted into a major portion of gasoline containingless than 100 ppm sulfur and nitrogen, and a minor portion of residualfuel oil containing about 1 percent or less sulfur; which processcomprises:

a. hydrocracking heavy hydrocarbon oil charge, in a first hydrocrackingzone, with molecular hydrogen at a temperature in the range of fromabout 700850F. in the presence of a sulfur and nitrogen resistanthydrocracking catalyst comprising a hydrogenation component supportedupon a cracking base consisting of an amorphous inorganic oxide havingpore size distribution in the range of at least 20-200 angstrom unitsfor conversion of said heavy hydrocarbon oil charge into not more thanabout percent gasoline fraction, a major portion of gas-oil fractionboiling in the range of 430l000F., and at least about percent residualoil fraction boiling above l00OF. containing about 1 percent or lesssulfur;

b. separating, in a separation zone, the gas-oil fraction from theresidual oil fraction;

c. recovering at least a portion of said residual fraction as low sulfurheavy fuel oil product; and

d. hydrocracking the gas-oil fraction in a second hydrocracking zonewith molecular hydrogen at a temperature in the range of about 700F. toabout 780F., in the presence of a sulfur and nitrogen resistanthydrocracking catalyst to produce gasoline boiling in the range of55430F. and containing I00 ppm or less sulfur and nitrogen.

2. The process of claim 1 wherein a portion of the residual fraction isrecycled from the separation zone to the first hydrocracking zone forconversion into additional gas-oil fraction, and wherein residual fueloil yield from the separation zone is equivalent to at least l0 percentof the residual fraction boiling above [000F. contained in the heavyhydrocarbon oil charge.

3. The process ofclaim 2 wherein the residual fuel oil product isequivalent to at least percent of the residual fraction boiling abovelO00F. contained in the heavy hydrocarbon oil charge.

4. The process of claim 3 wherein the gas-oil fraction is partiallyconverted to gasoline in the second hydrocracking zone, whereinunconverted gas-oil fraction is separated from gasoline and wherein saidunconverted gas-oil fraction is recycled to the second hydrocrackingzone for conversion into additional gasoline.

5. The process of claim 4 wherein liquid effluent from the secondhydrocracking zone, comprising gasoline, dry gas and unconverted gas-oilfraction is charged along with liquid effluent from the firsthydrocracking zone comprising gas-oil fraction, residual fraction, and asmall amount of gasoline and dry gas, to

the separation zone, wherein said first and second hydrocracking zoneliquid effluent is separated into a dry gas fraction, gasoline, agas-oil fraction, and a residual fraction.

6. The process of claim 5 wherein the hydrocracking catalyst in thefirst hydrocracking zone comprises a sulfur and nitrogen resistanthydrogenation component selected from the group consisting of Group Vlmetals, Group Vlll metals, their oxides, their sulfides, and mixturesthereof, supported upon an amorphous metal oxide cracking base selectedfrom the group consisting of alumina, silica-alumina, silica-zirconia,silica-titania, and mixtures thereof.

7. The method of claim 6 wherein the hydrocracking catalyst employed inthe second hydrocracking zone comprises a hydrogenation componentselected from the group consisting of Group Vl metals, Group VIIImetals, their oxides, their sulfides, and mixtures thereof, and aninorganic oxide cracking base selected from the group consisting ofalumina, silica-alumina, silica-zirconia, silica-titania, a cationexchanged crystalline silica-alumina zeolitic molecular sieve havinguniform pore openings in the range of from about 5 angstroms to about 20angstroms, and mixtures thereof.

8. The process of claim 7 wherein the hydrocracking catalyst containedin the first hydrocracking zone comprises a hydrogenation componentselected from the group consisting of a cobalt-molybdenum mixture, acobalt oxide-molybdenum oxide mixture, a cobalt sulfide-molybdenumsulfide mixture, a nickel-cobaltmolybdenum mixture, a nickeloxide-cobalt oxidemolybdenum oxide mixture, and a nickel sulfide-cobaltsulfide-molybdenum sulfide mixture, and wherein the amorphous metaloxide cracking base is selected from the group consisting of alumina andsilica-alumina.

9. The process of claim 8 wherein the hydrogenation component of thehydrocracking catalyst contained in the second hydrocracking zone isselected from the group consisting of a nickel-tungsten mixture, anickel oxide-tungsten oxide mixture, a nickel sulfide-tungsten sulfidemixture, a cobalt sulfide-molybdenum sulfide mixture, and a nickelsulfide-cobalt sulfidemolybdenum sulfide mixture and wherein theinorganic oxide cracking base is selected from the group consisting ofalumina, silica-alumina, and a cation exchanged crystallinesilica-alumina zeolitic molecular sieve having uniform pore openings inthe range of from about 5 angstroms to about 20 angstroms, and mixturesthereof.

10. The process of claim 9 wherein the exchanged cations of the zeoliticmolecular sieve are selected from the group consisting of hydrogen,ammonia, calcium, magnesium, zinc, and mixtures thereof, and whereinsaid zeolitic molecular sieve contains from about 0 to about 5 percentweight sodium cations.

11. The method of claim 10 wherein a small portion of the gas-oilfraction is recycled to the first hydrocracking zone as a wash oil.

12. A hydrocracking process for the conversion of a heavy hydrocarboncharge oil containing 0. l-4 percent sulfur, -1000 ppm or more nitrogen,and 100 ppm or more compounds of nickel, vanadium, iron and copper, andcomprising from about I0 to 50 volume percent residual fraction boilingabove l000F. into residual fuel oil containing 0-l percent sulfur andgasoline containing -l00 ppm sulfur and nitrogen; which proto about10,000 scf/b, a pressure of from about 500 cess comprises: to about2,500 psig, a liquid hourly space velocity at. treating said heavyhydrocarbon oil, in a first hyof from about 0.5 to about 8.0 volumes ofoil per drocracking Zone. with m lecular hy oge in a hour per volume ofcatalyst, at temperature of from hydrogen to hydrocarbon of about LSCf/b about 700 to about 790F., in the presence ofa byabout 15,000 atPressure of from about drocracking catalyst comprising a hydrogenation500 to about 3,000 p liquid hourly Space component selected from thegroup consisting of a locity of from about 0.1 to about 10.0 volumes ofcharge per hour per volume of catalyst, a temperature of from about700-850F. in the presence of 10 a hydrocracking catalyst consisting of ahydrogenation component selected from the group consisting of cobalt,molybdenum, nickel, their oxides, their sulfides, and mixtures thereof,and an amorphous metal oxide cracking base selected from the groupconsisting of alumina, silica-alumina, silicazirconia, silica-titania,and mixtures thereof, to partially convert said heavy hydrocarbon oilinto 0-5 percent gasoline boiling in the range 55-430F; a

. ()100 ppm sulfur and nitrogen. ma or portion of gas 01' boiling in therange of 4300 IOOOOF and at least 10 volume percent 13. The method ofclaim 12 wherein effluent from Sidual oil boiling above 100001;; thesecond hydrocracking reaction zone comprises unb. separating effluentfrom the first hydrocracking convefted low sulfur gasolme and zone intoa gas-oil fraction and a residual fraction; wherein emufmt from f firstlllydroc'jackmg zone c. recycling a first portion of the separatedresidual comprlses resfldual fracnon, fracuon, and 0 5 fraction to thefirst hydrocracking zone for conver' percent gasoline and dry gas,wherein effluent from the Sion into additional first hydrocracking zoneand from the second hydrod. yielding a second portion of the separatedresidual cracking Zone are separated in a separation Zone into fractionsufficient to limit the conversion of the redry gas, gasoline, fractionand a residual frac- 5idua| fractio ili above |0OOF f the heavy tion,wherein the gas-oil fraction from the separation hydrocarbon oil chargeinto gas-oil fraction to Zone, comprising 8 from the first hydrocrackingabout 80 volume percent as heavy fuel oil containzone and unconvertedgas-oil from the second hydroing 0-1 percent sulfur; and cracking zoneis charged to the second hydrocracking e. contacting separated gas-oil,in a second hydrozone for conversion into gasoline and wherein gasolinecracking zone, with molecular hydrogen in a hy- 35 from the separationzone is recovered as product. drogen to hydrocarbon ratio of from about1,000

cobalt oxide-molybdenum oxide mixture, a cobalt sulfide-molybdenumsulfide mixture, a nickel sulfide-tungsten sulfide mixture, a nickeloxidetungsten oxide mixture, and a nickel-tungsten mixture, and aninorganic cracking base selected from the group consisting of alumina,silicaalumina, a cation exchanged crystalline silica-alumina zeoliticmolecular sieve having uniform pore openings in the range of from about5 to about 20 angstrom units, and mixtures thereof, to convert saidseparated gas-oil fraction into gasoline containing

1. A HYDROTREATING PROCESS WHEREIN HEAVY HYDROCARBON OIL CHARGECONTAINING 0.1 TO 8 PERCENT SULFUR, 100 TO 1000 PPM AND MORE NITROGEN,AND 100PPM AND MORE COMPOUNDS OF NICKEL, VANADIUM, IRON AND COPPER, ANDCOMPRISING FROM BOUT 10 TO 50 VOLUME PERCENT RESIDUAL FRACTION BOILINGABOVE 1000*F ARE CONVERTED INTO A MAJOR PORTIOON OF GASLINE CONTAININGLESS THAN 100PPM SULFUR AND NITROGEN, AND A MINOR PORTION OF RESIDUALFUEL OIL CONTANING ABOUT 1 PERCENT OR LESS SULFUR; WHICH PROCESSCOMPRISES: A. HYDROCRACKING HEAVY HYDROCARBON OIL CHARGE, IN A FIRSTHYDROCRACKING ZONE, WITH MOLECULAR HYDROGEN AT A TEMPERATURE IN THERANGE OF FROM ABOUT 700*-850*F IN THE PRESENCE OF A SULFUR AND NITROGENRESISTANT HYDROCRACKING CATALYST COMPRISING A HYDROGENATION COMPONENTSUPPORTED UPON A CRACKING BASE CONSISTING OF AN AMORPHOUS OF AT EAST20-200 ANGSTROM UNITS FOR CONVERSION OF SAID INORGANIC OXIDE HAVING PORESIZE DISTRUBITION IN THE RANGE HEAVY HYDROCARBON OIL CHARGE INTO NOTMORE THAN ABOUT 5 PERCENT GASOLINE FRACTION, A MAJOR PORTION OF GAS-OILFRACTION BOILING IN THE RANGE OF 430*-1000*F, AND AT LEAST ABOUT 10PERCENT RESIDUAL OIL FRACTION BOILING ABOVE 1000*F. CONTAINING ABOUT 1PERCENT OR LESS SULFUR; B. SEPARATING, IN A SEPARATION ZONE, THE GAS-OILFRACTION FROM THE RESIDUAL OIL FRACTION; C. RECOVERING AT LEAST APORTION OF SAID RESIDUAL FRACTION AS LOW SULFUR HEAVY FUEL OIL PRODUCT;AND D. HYDROCRACKING THE GAS-OIL FRACTION IN A SECOND HYDROCRACKING ZONEWITH MOLECULAR HYDROGEN AT A TEMPERATURE IN THE RANGE OF ABOUT 700*F TOABOUT 780*F IN THE PRESENCE OF A SULFUR AND NITROGEN RESISTANTHYDROCRACKING CATALYST TO PRODUCE GASOLINE BOILING IN THE RANGE OF55*-430*F AND CONTAINING 100PPM OR LESS SULFUR AND NITROGEN.
 2. Theprocess of claim 1 wherein a portion of the residual fraction isrecycled from the separation zone to the first hydrocracking zone forconversion into additional gas-oil fraction, and wherein residual fueloil yield from the separation zone is equivalent to at least 10 percentof the residual fraction boiling above 1000*F. contained in the heavyhydrocarbon oil charge.
 3. The process of claim 2 wherein the residualfuel oil product is equivalent to at least 20 percent of the residualfraction boiling above 1000*F. contained in the heavy hydrOcarbon oilcharge.
 4. The process of claim 3 wherein the gas-oil fraction ispartially converted to gasoline in the second hydrocracking zone,wherein unconverted gas-oil fraction is separated from gasoline andwherein said unconverted gas-oil fraction is recycled to the secondhydrocracking zone for conversion into additional gasoline.
 5. Theprocess of claim 4 wherein liquid effluent from the second hydrocrackingzone, comprising gasoline, dry gas and unconverted gas-oil fraction ischarged along with liquid effluent from the first hydrocracking zonecomprising gas-oil fraction, residual fraction, and a small amount ofgasoline and dry gas, to the separation zone, wherein said first andsecond hydrocracking zone liquid effluent is separated into a dry gasfraction, gasoline, a gas-oil fraction, and a residual fraction.
 6. Theprocess of claim 5 wherein the hydrocracking catalyst in the firsthydrocracking zone comprises a sulfur and nitrogen resistanthydrogenation component selected from the group consisting of Group VImetals, Group VIII metals, their oxides, their sulfides, and mixturesthereof, supported upon an amorphous metal oxide cracking base selectedfrom the group consisting of alumina, silica-alumina, silica-zirconia,silica-titania, and mixtures thereof.
 7. The method of claim 6 whereinthe hydrocracking catalyst employed in the second hydrocracking zonecomprises a hydrogenation component selected from the group consistingof Group VI metals, Group VIII metals, their oxides, their sulfides, andmixtures thereof, and an inorganic oxide cracking base selected from thegroup consisting of alumina, silica-alumina, silica-zirconia,silica-titania, a cation exchanged crystalline silica-alumina zeoliticmolecular sieve having uniform pore openings in the range of from about5 angstroms to about 20 angstroms, and mixtures thereof.
 8. The processof claim 7 wherein the hydrocracking catalyst contained in the firsthydrocracking zone comprises a hydrogenation component selected from thegroup consisting of a cobalt-molybdenum mixture, a cobaltoxide-molybdenum oxide mixture, a cobalt sulfide-molybdenum sulfidemixture, a nickel-cobalt-molybdenum mixture, a nickel oxide-cobaltoxide-molybdenum oxide mixture, and a nickel sulfide-cobaltsulfide-molybdenum sulfide mixture, and wherein the amorphous metaloxide cracking base is selected from the group consisting of alumina andsilica-alumina.
 9. The process of claim 8 wherein the hydrogenationcomponent of the hydrocracking catalyst contained in the secondhydrocracking zone is selected from the group consisting of anickel-tungsten mixture, a nickel oxide-tungsten oxide mixture, a nickelsulfide-tungsten sulfide mixture, a cobalt sulfide-molybdenum sulfidemixture, and a nickel sulfide-cobalt sulfide-molybdenum sulfide mixtureand wherein the inorganic oxide cracking base is selected from the groupconsisting of alumina, silica-alumina, and a cation exchangedcrystalline silica-alumina zeolitic molecular sieve having uniform poreopenings in the range of from about 5 angstroms to about 20 angstroms,and mixtures thereof.
 10. The process of claim 9 wherein the exchangedcations of the zeolitic molecular sieve are selected from the groupconsisting of hydrogen, ammonia, calcium, magnesium, zinc, and mixturesthereof, and wherein said zeolitic molecular sieve contains from about 0to about 5 percent weight sodium cations.
 11. The method of claim 10wherein a small portion of the gas-oil fraction is recycled to the firsthydrocracking zone as a wash oil.
 12. A hydrocracking process for theconversion of a heavy hydrocarbon charge oil containing 0.1-4 percentsulfur, 100-1000 ppm or more nitrogen, and 100 ppm or more compounds ofnickel, vanadium, iron and copper, and comprising from about 10 to 50volume percent residual fraction boiling above 1000*F. into residualfuel oil containing 0-1 percent sulfur and gasoline containing 0-100 ppmsulfur and nitrogen; which process comprises: a. treating said heavyhydrocarbon oil, in a first hydrocracking zone, with molecular hydrogenin a hydrogen to hydrocarbon ratio of about 1,000 scf/b to about 15,000scf/b, at a pressure of from about 500 to about 3,000 psig, a liquidhourly space velocity of from about 0.1 to about 10.0 volumes of chargeper hour per volume of catalyst, a temperature of from about 700*-850*F.in the presence of a hydrocracking catalyst consisting of ahydrogenation component selected from the group consisting of cobalt,molybdenum, nickel, their oxides, their sulfides, and mixtures thereof,and an amorphous metal oxide cracking base selected from the groupconsisting of alumina, silica-alumina, silica-zirconia, silica-titania,and mixtures thereof, to partially convert said heavy hydrocarbon oilinto 0-5 percent gasoline boiling in the range 55*-430*F; a majorportion of gas oil boiling in the range of 430*-1000*F., and at least 10volume percent residual oil boiling above 1000*F.; b. separatingeffluent from the first hydrocracking zone into a gas-oil fraction and aresidual fraction; c. recycling a first portion of the separatedresidual fraction to the first hydrocracking zone for conversion intoadditional gas-oil; d. yielding a second portion of the separatedresidual fraction sufficient to limit the conversion of the residualfraction boiling above 1000*F. of the heavy hydrocarbon oil charge intogas-oil fraction to about 80 volume percent as heavy fuel oil containing0-1 percent sulfur; and e. contacting separated gas-oil, in a secondhydrocracking zone, with molecular hydrogen in a hydrogen to hydrocarbonratio of from about 1,000 to about 10,000 scf/b, a pressure of fromabout 500 to about 2,500 psig, a liquid hourly space velocity of fromabout 0.5 to about 8.0 volumes of oil per hour per volume of catalyst, atemperature of from about 700* to about 790*F., in the presence of ahydrocracking catalyst comprising a hydrogenation component selectedfrom the group consisting of a cobalt oxide-molybdenum oxide mixture, acobalt sulfide-molybdenum sulfide mixture, a nickel sulfide-tungstensulfide mixture, a nickel oxide-tungsten oxide mixture, and anickel-tungsten mixture, and an inorganic cracking base selected fromthe group consisting of alumina, silica-alumina, a cation exchangedcrystalline silica-alumina zeolitic molecular sieve having uniform poreopenings in the range of from about 5 to about 20 angstrom units, andmixtures thereof, to convert said separated gas-oil fraction intogasoline containing 0-100 ppm sulfur and nitrogen.
 13. The method ofclaim 12 wherein effluent from the second hydrocracking reaction zonecomprises unconverted gas-oil, low sulfur gasoline, and dry gas, whereineffluent from the first hydrocracking zone comprises residual fraction,gas-oil fraction, and 0-5 percent gasoline and dry gas, wherein effluentfrom the first hydrocracking zone and from the second hydrocracking zoneare separated in a separation zone into dry gas, gasoline, a gas-oilfraction and a residual fraction, wherein the gas-oil fraction from theseparation zone, comprising gas-oil from the first hydrocracking zoneand unconverted gas-oil from the second hydrocracking zone is charged tothe second hydrocracking zone for conversion into gasoline and whereingasoline from the separation zone is recovered as product.